Low power integrated circuit (IC) design becomes more and more important in various applications. Integrated circuits may include multiple blocks. Some blocks in the integrated circuit are often shut down when they are not actively in use to reduce leakage power. However, under some circumstances, certain circuit units within these blocks that are to be shut down may need to stay power-on. For example, certain buffers need to be powered on for some signals (e.g., power switch control signals, clock signals, feed through signals, etc.). In addition, isolation cells or level shifters often need to be powered on.